1. Field of the Invention
This invention relates to hydraulic pumping systems which are charged by the actuation of a wheel rolling over a plunger of a pump, and particularly to such a pump and pumping system particularly adapted for rail wheels, for example of a passenger or freight train.
2. Discussion of the Prior Art
It is known to use the rolling energy of a wheel, for example of a train wheel, as the input energy for a hydraulic pump. For example, such devices are described in U.S. Pat. No. 4,334,596. In U.S. Pat. No. 4,334,596, a rail wheel rolls over a pump plunger, and as it does so, depresses the plunger. The plunger is connected to a hydraulic piston by a compression spring, so that when the spring compresses, the hydraulic piston shifts. After the wheel rolls over the plunger, the first spring returns the plunger to its extended position and the second spring returns the hydraulic piston to its extended position.
In this arrangement, the plunger returns to its normal extended position under all conditions. Thus, even after the pump has been operated to produce the maximum system pressure, the plunger continues to be depressed by every wheel rolling over it. This results in needless hammering of the plunger every time a wheel rolls over it with attendant needless wear on sliding bearing surfaces of the pump, sliding seals and fatigue wear on the springs. In addition, the needless reciprocation of the plunger adds to needless energy input to the pump, which undesirably generates additional heat in the system.